In recent years there has been intense interest in the dental field in adhesives that bond to hard tissues such as dentin. Many of these adhesives have been used in conjunction with an acid pretreatment of the dentin prior to application of the adhesive. A very wide variety of acids have been tried, with phosphoric, citric and oxalic acids being particularly popular pretreatments. The use of such acids, especially phosphoric acid, has not been without controversy. The American Dental Association has recommended against phosphoric acid pretreatment of dentin. However, phosphoric acid is extensively used as a pretreatment in Japan in conjunction with dentin adhesives from Kuraray Company, Ltd. Citric acid has a less severe etching effect than phosphoric acid and is used as a dentin pretreatment in the U.S. in conjunction with a dentin adhesive sold by Den-Mat Corporation. Oxalic acid also has a less severe etching effect than phosphoric acid, and the use of its monoacid and certain of its salts as a pretreatment is described in U.S. Pat. No. 4,538,990. Other references describing various pretreatments for dentin include M. Buonocore, W. Wileman, and F. Brudevold, J. Dent. Res., 35, 846 (1956 ), M. Buonocore and M. Quigley, J. Amer. Dent. Assoc., 57, 807 (1958), Public Health Service Publication No. 1494, "Adhesive Restorative Dental Materials--II", pp. 103-155 (1966), M. Buonocore, "The Challenge of Bonding to Dentin", The Acid Etch Technique, (St. Paul, 1974), N. Nakabayashi, K. Kojima, and E. Masuhara, J. Bio. Mat. Res., 16, 265-273 (1982), K. Nagata, T. F. Lundeen, and P. T. Turner, J. Bio. Mat. Res., 18, 1089-1103 (1984), R. L. Bowen, R. L. Blosser, and A. D. Johnston, Abstract No. 915, p. 276, AIDR/AADR Abstracts 1985 (Paper presented Mar. 22, 1985), E. C. Munksgaard and E. Asmussen, J. Dent. Res., 63, (8): 1087-1089 (1984), E. C. Munksgaard, M. Irie, and E. Asmussen, J. Dent. Res., 64 (12): 1409-1411 (1985), U.S. Pat. Nos. 3,200,142, 4,259,075, 4,259,117, 4,368,043, 4,383,052, 4,443,197, 4,499,251, 4,537,940, and 4,539,382, and Danish Pat. Appl. No. 4898-83.
In addition, many phosphorus-based adhesives have been applied to dentin or enamel. Many of these adhesives have some degree of acidity and may, in some cases, cause mild etching of dentin or enamel. Examples of such adhesives include many of the phosphorus compounds described in the above-mentioned references, as well as those shown in U.S. Pat. Nos. 3,882,600, 3,997,504, 4,182,035, 4,222,780, 4,235,633, 4,404,150, 4,514,342, 4,515,930, 4,544,467, European Published Pat. Appl. Nos. 0 058 483 and 0 155 812, and Japanese Laid-Open Pat. Appl. (Kokai) Nos. 57-14372 and 57-167364.
Several of the above-mentioned references stress that enhanced adhesion to dentin and/or protection from microleakage can be obtained if the pretreatment results in deposition of insoluble calcium salts on the surface of the dentin (see, e.g., U.S. Pat. No. 4,538,990).
A reference of collateral interest to the instant invention, although not itself dealing with the priming of hard tissue, is U.S. Pat. No. 4,525,511. It describes a primer for high solids enamel automotive finishes.